In time-division multiplex (TDM) systems the encoded or non-encoded samples of the information (speech) supplied by a subscriber occupy time slots in consecutive frames of time slots. The connection established between two participants (for example via a time switching system or T-switch) results in the information contained in the relevant time slots of the two subscribers being mutually interchanged. If it is desired to establish a connection between three subscribers, a more complicated treatment and processing of the information stored in the (three) time slots per frame is required.
From German Patent Application No. 2918086, which has been laid open to public inspection, it is known to establish a conference connection between three participants by sequentially entering the information (speech samples) of the three subscribers A, B, C into one and the same memory location of a first memory. After the sample from A has been written into the first memory this sample (from A) is entered in the same location in a second memory and the sample from B is written into the first memory. When the sample from C is applied to the first memory the location in which sample B and the location in which sample A has been written is addressed by one addressing memory and the information stored in the first memory (sample from B) is added to the information in the second memory (sample from A) and transmitted in the outgoing time slot of subscriber C. This same cycle is thereafter performed for the subscribers A and B and is repeated thereafter, starting with C.
This method requires that the connection memory (first memory) which must be present in any case must be extended by a similar, additional memory, (second memory) which entails additional expense.